Abstract 218: Nitrative Thioredoxin Inactivation as a cause of Enhanced Myocardial Ischemia/Reperfusion Injury in Aging Heart
It is well-recognized that myocardial ischemia/reperfusion (MI/R) injury (e.g, cardiomyocyte apoptosis) is significantly increased in older individuals. Several recent studies have demonstrated that thioredoxin (Trx) is an important anti-apoptotic/cytoprotective molecule. The present study was designed to determine whether Trx activity is altered in aging heart, thus contributing to increased susceptibility to MI/R. Compared with young animals (3 month), MI/R-induced cardiac injury was markedly enhanced in aging mice (20 month) as evidenced by increased apoptosis (TUNEL: 5.0±1.8 % vs. 8.8±0.9%, caspase 3 activity: 18±1.7 vs. 25.1±0.9 nmol/h/mg protein, P<0.01) and increased infarct size (38.5±2.7% vs. 52.0±1.8%, P<0.01). Trx activity was markedly decreased in the aging heart before MI/R (27.8% lower than young, P<0.05) and this difference was further amplified after MI/R (54.9% lower than young, P<0.01). Surprisingly, Trx expression was not significantly changed, indicating that reduced Trx activity in the aging heart cannot be attributed to reduced Trx expression. Interestingly, Trx nitration, a post-translational modification that inhibits Trx activity, was significantly increased in the aging heart (74.4±3.1 vs. 51.9±5.1 AU in young heart, P<0.01). Moreover, Trx-ASK1 complex formation, a mechanism by which Trx inhibits apoptosis, was significantly reduced (P<0.01) and subsequently, the activity of p38 MAPK, a pro-apoptotic downstream molecule for ASK1, was significantly increased in the aging heart (P<0.01). To further establish a causative link between nitrative Trx inactivation and increased MI/R injury in the aging heart, FP15 (a peroxynitrite decomposition catalyst, 5 mg/kg, ip.) was administered in aging animals 10 min before R. Treatment with FP15 markedly reduced Trx nitration, increased Trx activity, restored Trx-ASK1 interaction, reduced P38 MAPK activity, attenuated caspase 3 activation and reduced infarct size in aging animals (p<0.01). Taken together, our results demonstrated that Trx activity is decreased in the aging heart by post-translational nitrative modification. Interventions that restore Trx activity in the aging heart may be a novel therapy to attenuate MI/R injury in aging patients.